In characterizing the physical and chemical behavior of substances, it is customary to separately investigate both their thermodynamic (e.g., calorimetric) and their structural (e.g. crystallographic) properties.
Thermodynamic properties are commonly determined by differential scanning calorimetry (DSC) and by differential thermal analysis (DTA). Modern DSC and DTA instruments are highly advanced, affording sensitive temperature regulation and measurement, often to a fraction of a Centigrade degree. A sample may be heated rapidly through a wide temperature range, and calorimetric output measured with precision, over a period of a very few minutes.
Crystallographic properties are often studied by X-ray diffraction (XRD) spectrometry. To achieve high resolution, diffraction data have been collected on photographic film, or with scintillation counters. Such procedures are slow, requiring data collection times of thirty minutes or more for each pattern at each temperature. A single scan over a range of temperatures may consume most of a day or longer. Because of the slow data collection times for X-ray diffraction scans, structural and calorimetric data could not be correlated for fast processes. In industrial processes, heat and/or chemical treatments often occur in a matter of a few minutes or seconds (i.e. the extrusion of a polymer or the oxidation of a catalyst). In addition, the equipment for heating samples in X-ray diffraction analysis has been comparatively crude, e.g., uniform sample temperature control within five degrees has been attainable only rarely except near room temperature. For both reasons, rapid scanning, i.e., dynamic reading of a series of X-ray diffraction patterns correlated accurately and simultaneously with temperature rise as a sample is heated, has not been previously practiced.
Instead, the usual approach has been to analyze a sample first by one of the foregoing techniques and then by the other. Data from the two determinations were correlated as best might be, to elucidate as far as possible the thermostructural behavior of the sample. However, due to the differences in sample heating conditions and sample size, and in the data collection times between DSC and conventional XRD, the diffraction and calorimetric data did not correlate well when trying to assign an observed structural change to a particular calorimetric event. In applying this method to multi-component samples, separate physicochemical phenomena occurring at closely spaced temperatures were often missed or misinterpreted as were indications of transitory species and irreversible phase changes occurring over a period of a minute or two.
More recently, one aspect of this situation has been improved. Position sensitive detectors have been developed as X-ray detectors, dramatically increasing the speed of acquiring diffraction data. With them, the time scale for X-ray diffraction analysis can be shortened to be compatible with that of differential thermal analysis and differential scanning calorimetry.
The present invention takes advantage of this improvement and provides a workable instrument and method for simultaneous dynamic observation of thermodynamic and structural properties of a sample undergoing temperature and/or environmental change.